When testing flight vehicles, it is often necessary or beneficial to obtain knowledge of the prevailing wind conditions near the flight path. Existing methods of wind measurement normally supply results in specific points that are either located at considerable distances from the actual flight path or do not give measurements at a the correct time. Around an airport or testing site there is a need for monitoring continuously the wind conditions.
The existing methods of wind measurement are based on a wide variety of principles. Typical meteorological methods include the use of different types of anemometers, balloons, etc. Special testing methods may use smoke emission or other optical means. Most known acoustic methods and devices are based, either on measuring the signal propagation speed, i.e. the speed of sound+the wind speed, or the Doppler effect. In particular, ultrasonic anemometers and sodar systems use these principles. Several such methods and suitable devices are disclosed in U.S. patents U.S. Pat. No. 3,379,060 (time), U.S. Pat. No. 4,031,756 (ultrasonic), U.S. Pat. No. 3,693,433 (ultrasonic anemometer), U.S. Pat. No. 4,038,870 (ultrasonic), the published West German patent application DE-A 1 523 248 (signal propagation time), U.S. patents U.S. Pat. No. 4,286,462 (sodar), U.S. Pat. No. 4,882,931 (air flow), U.S. Pat. No. 4,891,976 (resonance chamber), U.S. Pat. No. 4,890,488 (ultrasonic anemometer), and the French patents FR 1.012.054 and FR 1.142.353 (compressible air flow).